Methane emissions and 13C composition from beef steers consuming binary C3-C4 diets

Area of Science:

• Agricultural Science
• Animal Science
• Environmental Science

Background:

• Improving forage quality can reduce methane emission intensity in ruminants.
• Legumes are often explored for their potential to enhance forage nutritive value and mitigate enteric methane emissions.

Purpose of the Study:

• To evaluate the impact of rhizoma peanut (Arachis glabrata; RP) inclusion in bahiagrass (Paspalum notatum) hay diets on intake and methane (CH4) production in beef steers.
• To assess the utility of enteric CH4 δ13C for estimating the proportion of RP contribution to emissions.

Main Methods:

• Twenty-five Angus-crossbred steers were fed diets with varying proportions of RP and bahiagrass hay (0% to 100% RP).
• Methane emissions were quantified using the sulfur hexafluoride (SF6) tracer technique.
• Apparent total tract digestibility was determined using indigestible neutral detergent fiber.
• A two-pool mixing model was employed to predict diet source contributions using CH4 δ13C analysis.

Main Results:

• Dietary inclusion of RP did not significantly affect steer intake or total CH4 production.
• Average CH4 production was 250 g CH4/d per animal and 33 g CH4/kg dry matter intake across all treatments.
• CH4 δ13C values became progressively more depleted (negative) with increasing RP proportion, showing a quadratic effect (P=0.04).
• Regression analysis demonstrated a strong relationship (Adj. R2=0.89) between predicted and observed RP proportions using CH4 δ13C, indicating its utility for tracking dietary contributions in C3-C4 forage systems.

Conclusions:

• While direct reduction in CH4 production was not observed with RP inclusion in this C4-based hay diet, the δ13C technique proved effective for monitoring dietary influences on enteric methane.
• The δ13C signature in enteric methane can serve as a reliable tool for estimating the contribution of different forage sources in mixed-diet scenarios.